Method of producing phosphate fertilizer

Abstract

To provide a phosphate fertilizer with a stable and high fertilizer effect and a method for producing the same.SOLUTION: There is provided a phosphate fertilizer produced by pulverization of a dephosphorized slag obtainable by dephosphorization of a high phosphorus molten iron, in which the concentration of P2O5 is 10 mass% or more, the ratio of concentration of CaO to P2O5, (CaO) / (P2O5), is 2.3 to 4.2, the ratio of concentration of SiO2 to P2O5, (SiO2) / (P2O5), is 0.6 to 1.3, and a soluble phosphoric acid rate is 80 mass% or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention is a phosphate fertilizer with excellent available phosphate ratio. Fee It relates to a manufacturing method. [Background technology]

[0002] Conventionally, dephosphorization slag produced by dephosphorization of hot metal containing high concentration of P contains a lot of phosphoric acid (P2O5) and is used as a raw material for phosphate fertilizer. Patent Document 1 discloses a raw material for phosphate fertilizer in which the slag contains, in mass% of a ternary system of CaO, P2O5, and SiO2, 50-65% CaO, 15% or more P2O5, and less than 10% SiO2. Patent Document 2 discloses a method for producing a raw material for phosphate fertilizer in which the amount of CaO-based dephosphorization agent injected together with oxygen gas is adjusted to obtain a composition containing 15% or more P2O5 so as to obtain slag with a basicity of 1.5 or more, and further, a silicon source is added from the top in the middle to final stages of blowing in the dephosphorization treatment to adjust the composition to a ternary system of CaO, P2O5, and SiO2 containing 10% or more SiO2.

[0003] Patent Document 3 also describes a slag containing 60 mass% or more of CaO, SiO2, P2O5, and iron oxide (Fe equivalent) in total, with a basicity α expressed as the mass concentration ratio of CaO to SiO2 of 1.5 to 3.0, and a P2O5 content of 8 mass% or more (-4α 2 Patent Document 4 discloses a phosphate fertilizer raw material containing SiO2 / P2O5≧0.4, CaO / P2O5≧2.0, P2O5≧10%, and T.Fe: 5% to 15% by mass or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-140294 A [Patent Document 2] JP 2015-140473 A [Patent Document 3] JP 2016-88757 A [Patent Document 4] JP 2017-128747 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, as in the techniques described in Patent Documents 1 to 4 above, the composition ranges proposed for phosphate fertilizers are varied and wide-ranging, and the fertilizer effect cannot be fully guaranteed at present.

[0006] In view of the above problems, the present invention provides a phosphate fertilizer with a stable and high fertilizer effect. Fee The object is to provide a manufacturing method. [Means for solving the problem]

[0007] Conventionally, the soluble phosphate ratio is generally used as an index for evaluating the effect of phosphate fertilizer. The soluble phosphate ratio is the ratio of the phosphoric acid content in the fertilizer that dissolves in a 2% citric acid solution. Here, since citric acid is a strong acid with a pH of 2 to 3, the pH is lower than that of the actual soil environment. Therefore, the inventors of the present invention believe that the reason why the fertilizer effect of conventional phosphate fertilizers cannot be fully guaranteed is because the fertilizer effect is evaluated based on the phosphoric acid content dissolved in a citric acid solution, and have considered using the soluble phosphate ratio as an index for the fertilizer effect. The soluble phosphate ratio is the ratio of the phosphoric acid content in the fertilizer that dissolves in a 2% ammonium citrate solution, and ammonium citrate has a pH of 6 to 7, which is closer to the soil environment. Therefore, the solubility can be said to be an index that directly represents the ease of dissolving phosphoric acid into the actual soil.

[0008] Furthermore, the inventors noticed that solid solutions of silicocarnotite and nagelschmittite exhibit high fertilizer effects, and discovered in more detail the region with high soluble phosphate content in the CaO-SiO2-P2O5 ternary system, which led to the present invention.

[0009] The present invention is as follows. (1) Mass %: P 2 O 5 The concentration is 10% or more, and CaO and P 2 O 5 Concentration ratio (CaO) / (P 2 O 5 ) is 2.3 to 4.2, SiO 2 and P 2 O 5 Concentration ratio (SiO 2 ) / (P 2 O 5 ) is between 0.6 and 1.3 A method for producing a phosphate fertilizer, comprising the steps of: performing a dephosphorization process on the molten iron so that the P concentration in the molten iron after the dephosphorization process is 0.10% or more by mass% and the value Δ[P] obtained by converting the amount of P in the dephosphorization slag at the end of the dephosphorization process into the P concentration in the molten iron satisfies the condition of the following formula (1); Cooling and pulverizing the dephosphorization slag obtained by the dephosphorization treatment; A method for producing a phosphate fertilizer, comprising the steps of: 0.72×[Si] in ≦Δ[P]≦1.56×[Si] in (1) Where, [Si] in represents the total amount of Si in the dephosphorization slag and the molten iron during the dephosphorization treatment, converted into the Si concentration in the molten iron (mass%). (2) The target composition of dephosphorization slag and the [Si] in and determining the amount of the dephosphorization slag from the above, and determining the type and amount of the dephosphorization flux containing at least CaO. (1) A method for producing a phosphate fertilizer according to the above. Effect of the Invention

[0010] According to the present invention, it is possible to provide a phosphate fertilizer having a stable and high fertilizer effect and a method for producing the same. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram for explaining the difference in soluble phosphate ratio in a ternary system of CaO-SiO2-P2O5. [Diagram 2] FIG. 2 is a graph showing the relationship between the phosphoric acid concentration in dephosphorization slag and the P concentration in molten iron at equilibrium during dephosphorization treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In order to increase the soluble phosphoric acid ratio in dephosphorization slag, it is necessary to make phosphoric acid present as a solid solution in which phosphoric acid (P2O5) is soluble, i.e., silicocarnotite (5CaO-SiO2-P2O5) or nagelschmittite (7CaO-2SiO2-P2O5). In order to make all of the phosphoric acid in the slag exist as silicocarnotite, the molar ratio of CaO to P2O5 must be 5 times, i.e., the concentration ratio of CaO to P2O5 (CaO) / (P2O5) must be 1.97 or more in weight ratio, and the molar ratio of SiO2 to P2O5 must be 1 or more, i.e., the concentration ratio of SiO2 to P2O5 (SiO2) / (P2O5) must be 0.42 or more in weight ratio.

[0013] Figure 1 is a diagram to explain the difference in soluble phosphate ratio in the ternary system of CaO-SiO2-P2O5. As shown in Figure 1, if the slag composition is within the triangular region where the ratio (CaO) / (P2O5) ≥ 1.97 and the ratio (SiO2) / (P2O5) ≥ 0.42, the necessary condition for all P2O5 to become solid solution silicocarnotite is satisfied. Similarly, the necessary condition for all P2O5 to become solid solution nagelschmittite is within the triangular region where the ratio (CaO) / (P2O5) ≥ 2.76 and the ratio (SiO2) / (P2O5) ≥ 0.85, but this region is completely included in the region of silicocarnotite.

[0014] However, when the slag has a composition where the ratio (CaO) / (P2O5) is around 1.97 or the ratio (SiO2) / (P2O5) is around 0.42, the composition varies and there is a local shortage of CaO or SiO2 relative to P2O5. As a result, insoluble β-3CaO-P2O5 tends to precipitate rather than a solid solution, and the soluble phosphate ratio drops sharply.

[0015] On the other hand, it is thought that there are upper limits for the ratios (CaO) / (P2O5) and (SiO2) / (P2O5) to show a high soluble phosphate ratio. When the ratio (CaO) / (P2O5) becomes high, in addition to the solid solutions mentioned above, 2CaO-SiO2 and 3CaO-SiO2 with low phosphate concentrations and insoluble 3CaO-P2O5 with high phosphate concentrations are precipitated. Similarly, when the ratio (SiO2) / (P2O5) becomes high, CaO-SiO2 and SiO2 with low phosphate concentrations and insoluble 3CaO-P2O5 with high phosphate concentrations are precipitated. As a result, it is thought that if the ratios (CaO) / (P2O5) and (SiO2) / (P2O5) increase excessively, the soluble phosphate ratio will gradually decrease.

[0016] Based on the above conditions, the inventors conducted experiments and found that the soluble phosphate ratio peaks near the composition ratio of Nagelschmittite, and as shown in Figure 1, it was found that in dephosphorization slag, a soluble phosphate ratio of 80% or more can be obtained by setting the ratio (CaO) / (P2O5) to 2.3 to 4.2 and the ratio (SiO2) / (P2O5) to 0.6 to 1.3, in mass percent.

[0017] When the ratio (CaO) / (P2O5) is less than 2.3 or the ratio (SiO2) / (P2O5) is less than 0.6, insoluble β-3CaO-P2O5 may precipitate, which reduces the soluble phosphate ratio. When the ratio (CaO) / (P2O5) is more than 4.2 or the ratio (SiO2) / (P2O5) is more than 1.3, in addition to the solid solutions mentioned above, 3CaO-SiO2 or 2CaO-SiO2 with low phosphate concentration and insoluble 3CaO-P2O5 with high phosphate concentration, or CaO-SiO2 or SiO2 with low phosphate concentration and insoluble 3CaO-P2O5 with high phosphate concentration will precipitate, which reduces the soluble phosphate ratio.

[0018] Next, a method for producing a phosphate fertilizer according to the present invention will be described. First, molten pig iron with a high concentration of P is charged into a converter, dephosphorization flux is added, and oxygen is blown from a top blowing lance to perform a dephosphorization process. In order to ensure that the dephosphorization slag contains a high concentration of phosphorus as a result of the dephosphorization process, the P concentration in the molten pig iron after the dephosphorization process is set to 0.10 mass% or more. If the P concentration in the molten pig iron after the dephosphorization process is less than 0.10 mass%, the phosphorus concentration in the equilibrium dephosphorization slag drops sharply.

[0019] Figure 2 shows the relationship between the phosphoric acid concentration in the dephosphorization slag at equilibrium during dephosphorization and the P concentration in the hot metal. As mentioned above, there is an optimum region in the ternary system of CaO-SiO2-P2O5, and in this optimum region, the lower limit of the ratio (CaO) / (SiO2) is about 1.8. In order to ensure a phosphoric acid concentration of 10 mass% or more even under such low basicity conditions, as shown in Figure 2, it is clear that the P concentration in the hot metal after dephosphorization needs to be 0.10 mass% or more.

[0020] The amount of dephosphorization slag generated by the dephosphorization process varies depending on the Si concentration in the molten iron before the process, and in order to obtain a composition in the optimal region in the ternary system of CaO-SiO2-P2O5, the amount of dephosphorization can be calculated as a function of the Si concentration in the molten iron before the process. Here, the amount of dephosphorization slag generated by the dephosphorization process, SV (kg / t), can be calculated from the P balance and Si balance as shown in the following formula (2). SV=Δ[P]×10×(142 / 62) / ((P2O5) / 100) =[Si] in ×10×(60 / 28) / ((SiO2) / 100)···(2) Δ[P]=[P] in -[P] f (3)

[0021] Here, Δ[P] represents the amount of dephosphorization, i.e., the amount of P in the dephosphorization slag at the end of the dephosphorization process, converted into the P concentration in the molten iron (mass%), and [Si] in represents the total amount of Si in the dephosphorization slag and the molten iron during the dephosphorization process, converted into the Si concentration in the molten iron (mass%). in represents the total amount of P in the dephosphorization slag and molten iron during the dephosphorization process, converted into the P concentration in the molten iron (mass%), and [P] f represents the P concentration (mass%) in the molten iron at the end of the dephosphorization process. Substituting these values ​​to control the ratio (SiO2) / (P2O5) between 0.6 and 1.3, it is necessary to perform the dephosphorization process so that Δ[P] falls within the range of the following formula (4). 0.72×[Si] in ≦Δ[P]≦1.56×[Si] in (4)

[0022] As described above, the slag volume SV of the dephosphorization slag generated in the dephosphorization process is determined by the target composition of the dephosphorization slag and the initial Si concentration [Si]. inFrom this, the type and amount of dephosphorization flux can be determined. The type of dephosphorization flux contains at least CaO, and may contain other elements such as SiO2, MgO, and P2O5 for the purpose of adjusting the basicity and further improving the soluble phosphate ratio. Note that SiO2 and P2O5 added as dephosphorization flux are determined based on the Si concentration [Si] in the molten iron during the dephosphorization process. in and P concentration [P] in and use it in the calculation.

[0023] The dephosphorized slag produced by the above procedure can then be cooled and crushed to produce phosphate fertilizer. EXAMPLES

[0024] Next, an embodiment of the present invention will be described, but the conditions are merely examples of conditions for confirming the feasibility and effects of the present invention, and the present invention is not limited to the description of the embodiment. The present invention can be implemented in various ways to achieve the object of the present invention without departing from the gist of the present invention.

[0025] (First embodiment) The molten iron (P concentration: 0.60 mass%, Si concentration: 0.10 mass%) obtained by reducing steelmaking slag on the molten iron was charged into a 1-ton refining furnace, dephosphorization flux was added, and oxygen was blown in from the top lance at a total of 19 Nm 3 The dephosphorization flux used contained 18.3 kg / t of quicklime (CaO), 9.5 kg of lightly burnt dolomite, and 8.4 kg / t of silica sand (SiO2), with total CaO of 23.6 kg / t and total MgO of 3.4 kg / t. As a result of adding the above dephosphorization flux, the total amount of Si in the dephosphorization slag and the molten iron during the dephosphorization process was converted into the Si concentration in the molten iron ([Si] in ) was 0.49 mass%. On the other hand, since the dephosphorization flux did not contain phosphoric acid, the total amount of P in the dephosphorization slag and the molten iron during the dephosphorization process was converted to the P concentration in the molten iron ([P] in) was 0.60 mass%, the same as the P concentration in the molten iron before the dephosphorization treatment.

[0026] After dephosphorization, the molten iron temperature was 1420℃ and the P concentration in the molten iron after treatment was [P] f The slag content (SV) of the dephosphorization slag after the dephosphorization treatment was 61.9 kg / t.

[0027] The dephosphorization slag obtained by the dephosphorization process was then recovered from the converter, cooled, and analyzed for its composition, which was found to contain 38.1% CaO, 16.9% SiO2, 5.5% MgO, 2.2% MnO, and 15.7% P2O5 by mass. In other words, the basicity C / S was 2.25, the ratio CaO / P2O5 was 2.43, and the ratio SiO2 / P2O5 was 1.08. From these results, the amount of P in the dephosphorization slag at the end of the dephosphorization process was converted into the P concentration in the hot metal (Δ[P]), which was calculated to be 0.42% by mass.

[0028] The dephosphorized slag was then crushed to under 150 μm and magnetically separated. The soluble phosphate (phosphate dissolved in ammonium citrate solution) was analyzed to be 13.7% by mass, and the soluble phosphate ratio was 87.0%. A planting test was then conducted using the resulting fertilizer sample, and it was found that the yield was equal to or greater than that of commercially available fertilizer.

[0029] (Second Example) Molten iron was charged into the converter, dephosphorization flux was added, and oxygen was blown from the top lance at a total flow rate of 19 Nm 3 / t of ferrous iron was supplied to perform dephosphorization. At this time, molten iron with various P and Si concentrations was prepared, and the amount of dephosphorization was controlled by using various dephosphorization fluxes, to obtain the dephosphorization slag and molten iron shown in Table 1. The obtained dephosphorization slag was cooled and pulverized to under 150 μm, and magnetically separated, after which the soluble phosphoric acid was analyzed to calculate the soluble phosphoric acid ratio. It was evaluated that the effect of the present invention was obtained when the soluble phosphoric acid ratio was 80% or more. For reference, the citric acid soluble phosphoric acid ratio was also analyzed.

[0030] [Table 1]

[0031] The underlines in Table 1 indicate values ​​outside the scope of the present invention. As shown in Table 1, in Examples 1 to 4, the phosphoric acid concentration (P2O5) in the dephosphorization slag was 10 mass% or more, the ratio (CaO) / (P2O5) was 2.3 to 4.2, and the ratio (SiO2) / (P2O5) was 0.6 to 1.3, so that the soluble phosphoric acid rate was high.

[0032] In contrast, in Comparative Example 1, the soluble phosphorus rate was high, but the P concentration in the molten iron after dephosphorization [P] f was less than 0.10% by mass, the phosphoric acid concentration (P2O5) in the dephosphorization slag was less than 10% by mass, and the fertilizer effect was insufficient. In Comparative Examples 2 to 5, Δ[P] was outside the condition of the above formula (4) in relation to the Si concentration in the initial molten iron, and therefore at least one of the ratios (CaO) / (P2O5) and (SiO2) / (P2O5) was outside the condition of the present invention, and the soluble phosphoric acid rate was low.

Claims

1. A method for producing a phosphate fertilizer in which the P2O5 concentration is 10% or more by mass, the concentration ratio of CaO to P2O5, (CaO) / (P2O5), is 2.3 to 4.2, and the concentration ratio of SiO2 to P2O5, (SiO2) / (P2O5), is 0.6 to 1.3, performing a dephosphorization process on the molten iron so that the P concentration in the molten iron after the dephosphorization process is 0.10% or more by mass% and the value Δ[P] obtained by converting the amount of P in the dephosphorization slag at the end of the dephosphorization process into the P concentration in the molten iron satisfies the condition of the following formula (1); Cooling and pulverizing the dephosphorization slag obtained by the dephosphorization treatment; A method for producing a phosphate fertilizer, comprising the steps of: 0.72×[Yes] in ≦Δ[P]≦1.56×[Si] in ・・・(1) Here, [Si] in represents the total amount of Si in the dephosphorization slag and the molten iron during the dephosphorization treatment converted into the Si concentration in the molten iron (mass %).

2. The target composition of dephosphorization slag and the [Si] in 2. The method for producing a phosphate fertilizer according to claim 1, further comprising the steps of: determining the amount of the dephosphorization slag from the above; and determining the type and amount of the dephosphorization flux containing at least CaO.

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